Abstract
The invention relates to a method for controlling a prosthesis or orthesis of the lower extremity, which prosthesis or orthesis comprises an upper part (10) and a lower part (20) that is connected to the upper part (20) via a knee joint (1) and is mounted so as to be pivotable relative to the upper part (10) about a joint pin (15); wherein an adjustable resistance device (40) is situated between the upper part (10) and the lower part (20), by means of which resistance device a flexion resistance (Rf) in an early and middle standing phase is modified, during walking, on the basis of sensor data, following initial heel contact up to the middle standing phase; wherein, following the initial heel contact, the flexion resistance (Rf) is increased to a value at which further flexion is blocked or at least slowed; wherein the progression over time of the flexion resistance increase and/or the maximum achievable flexion angle (Af) is modified on the basis of the inclination of the ground or a height difference (ΔH) to be overcome.
Claims
1. A method for controlling a prosthesis or orthosis of the lower extremity, having an upper part (10) and having a lower part (20) which is connected to the upper part (20) via a knee joint (1) and is mounted so as to be pivotable relative to the upper part (10) about a joint axis (15), wherein there is arranged between the upper part (10) and the lower part (20) an adjustable resistance device (40) by means of which, during walking, a flexion resistance (Rf) is changed on the basis of sensor data in an early and mid stance phase after initial heel contact up to the mid stance phase, characterized in that, after the initial heel contact, the flexion resistance (Rf) is increased to a value at which further flexion is blocked or at least slowed, wherein the temporal profile of the flexion resistance increase and/or the maximum achievable flexion angle (Af) is changed in dependence on the inclination of the surface or a height difference (ΔH) to be overcome.
2. The method as claimed in claim 1, characterized in that the maximum achievable flexion angle (Af) and/or the flexion angle (Af) at which the maximum flexion resistance (Rf) is achieved is increased in the case of an increasingly steep surface.
3. The method as claimed in claim 1, characterized in that, in the case of an increasingly steep surface, the maximum flexion resistance (Rf) is reduced.
4. The method as claimed in claim 1, characterized in that the flexion block or the flexion resistance increase is maintained for a defined period of time, and then the flexion resistance (Rf) is reduced.
5. The method as claimed in claim 4, characterized in that the flexion resistance is reduced after the flexion block or after the flexion resistance increase if a measure of the transverse force in the lower part (20) exceeds a limit value dependent on the inclination of the surface and/or a leg cord (70) exceeds a forward inclination dependent on the inclination of the surface and/or a measure of the hip moment initially exceeds and then falls below a limit value.
6. The method as claimed in claim 5, characterized in that the measure of the transverse force is determined by means of a transverse force sensor or from a difference in transverse force components of an ankle moment and knee moment.
7. The method as claimed in claim 1, characterized in that the flexion resistance (Rf) is reduced after an increase to below a blocking level if a predefined flexion angle (Af) is exceeded.
8. The method as claimed in claim 1, characterized in that the inclination of the surface can be calculated from a vertical and/or horizontal distance travelled in the preceding swing phase by the knee joint (1), in particular by a reference point in the vicinity of the sole of the foot, or from the ratio of a vertical and horizontal distance travelled in the preceding swing phase by the knee joint (1), in particular by a reference point in the vicinity of the sole of the foot, as a displacement calculation criterion.
9. The method as claimed in claim 8, characterized in that the beginning of the stance phase to be controlled is determined on the basis of an axial force impulse, a plantar flexion acceleration and/or an ankle moment.
10. The method as claimed in claim 1, characterized in that the inclination of the surface is calculated from an evaluation of a flexion angle (Af) and of an absolute angle of the upper part (10) or of the lower part (20) or from the evaluation of two absolute angles of the upper part (10) and lower part (20), as a kinematic criterion.
11. The method as claimed in claim 10, characterized in that the knee angular velocity and lower part angular velocity during walking are determined, and the quotient of the two angular velocities is calculated therefrom, wherein the inclination of the surface is determined on the basis of the change of the quotient of the angular velocities.
12. The method as claimed in claim 8, characterized in that the displacement calculation criterion and the kinematic criterion are used for determining the surface inclination.
13. The method as claimed in claim 1, characterized in that the position and/or orientation of a ground reaction force vector in relation to the orthosis or prosthesis is used as a control parameter.
14. The method as claimed in claim 1, characterized in that the detection of a roll-over of a foot part (30) over an edge prevents a flexion resistance increase or reduces the increased flexion resistance (Rf) again.
Description
[0025] Exemplary embodiments of the invention will be discussed in more detail below on the basis of the appended figures. In the figures:
[0026] FIG. 1—shows a schematic illustration of a prosthetic leg;
[0027] FIG. 2—shows an illustration of leg cords;
[0028] FIG. 3—shows a definition of a height difference when walking;
[0029] FIG. 4—shows an illustration of an inclination-dependent setting of the flexion angle and flexion resistance;
[0030] FIGS. 5a-5c—show different profiles of the flexion angle and flexion resistance at different surface inclinations;
[0031] FIG. 6—shows illustrations of the flexion angle and roll angle at different surface inclinations:
[0032] FIG. 7—shows illustrations of a kinematic criterion at different surface inclinations;
[0033] FIG. 8—shows an illustration of a geometric criterion when walking downward on a ramp, and
[0034] FIG. 9—shows an illustration of an orthosis.
[0035] FIG. 1 shows a schematic illustration of an artificial knee joint 1 in an application in a prosthetic leg. As an alternative to an application in a prosthetic leg, a correspondingly designed artificial knee joint 1 can also be used in an orthosis or an exoskeleton. Instead of replacing a natural joint, the artificial knee joint is then arranged medially and/or laterally on the natural joint. In the exemplary embodiment shown, the artificial knee joint 1 is in the form of a prosthetic knee joint having an upper part 10 with a side 11 which is anterior or situated in the walking direction or at the front, and a posterior side 12 which is located opposite the anterior side 11. A lower part 20 is arranged on the upper part 10 so as to be pivotable about a pivot axis 15. The lower part 20 also has an anterior side 21 or front side and a posterior side 22 or rear side. In the exemplary embodiment shown, the knee joint 1 is in the form of a monocentric knee joint, it is in principle also possible to control a polycentric knee joint in a corresponding manner. At the distal end of the lower part 20 there is arranged a foot part 30 which can be connected to the lower part either in the form of a rigid foot part 30 with a fixed foot joint or by a pivot axis 35, in order to make possible a movement sequence which emulates the natural movement sequence.
[0036] Between the posterior side 12 of the upper part 10 and the posterior side 22 of the lower part 20, the knee angle KA is measured. The knee angle KA can be measured directly by means of a knee angle sensor 25, which can be arranged in the region of the pivot axis 15. The knee angle sensor 25 can be coupled with a torque sensor or can have such a sensor, in order to detect a knee moment about the joint axis 15. On the upper part 10 there is arranged an inertial angle sensor or an IMU 51, which measures the spatial position of the upper part 10, for example in relation to a constant force direction, for example gravitational force G, which points vertically downward. An inertial angle sensor or an IMU 53 is likewise arranged on the lower part 20 in order to determine the spatial position of the lower part while the prosthetic leg is in use.
[0037] In addition to the inertial angle sensor 53, an acceleration sensor and/or transverse force sensor 53 can be arranged on the lower part 20 or on the foot part 30. By means of a force sensor or torque sensor 54 on the lower part 20 or on the foot part 30, an axial force FA acting on the lower part 20 or an ankle moment acting about the ankle joint axis 35 can be determined.
[0038] Between the upper part 10 and the lower part 20 there is arranged a resistance device 40 in order to influence a pivoting movement of the lower part 20 relative to the upper part 10. The resistance device 40 can be in the form of a passive damper, in the form of a drive, or in the form of a so-called semi-active actuator with which it is possible to store movement energy and purposively release it again at a later time in order to slow or assist movements. The resistance device 40 can be in the form of a linear or rotary resistance device. The resistance device 40 is connected to a control device 60, for example in a wired manner or via a wireless connection, which in turn is coupled with at least one of the sensors 25, 51, 52, 53, 54. The control device 60 electronically processes the signals transmitted by the sensors, using processors, computing units or computers. It has an electrical power supply and at least one memory unit in which programs and data are stored and in which a working memory for processing data is provided. After processing of the sensor data, an activation or deactivation command with which the resistance device 40 is activated or deactivated is outputted. By activation of an actuator in the resistance device 40 it is possible, for example, to open or close a valve or to generate a magnetic field, in order to change a damping behavior.
[0039] To the upper part 10 of the prosthetic knee joint 1 there is fastened a prosthesis socket, which serves to receive a thigh stump. The prosthetic leg is connected to the hip joint 16 by way of the thigh stump. On the anterior side of the upper part 10 a hip angle HA is measured, which is marked on the anterior side 11 between a vertical line through the hip joint 16 and the longitudinal extension of the upper part 10 and the connecting line between the hip joint 16 and the knee joint axis 15. If the thigh stump is lifted and the hip joint 16 is flexed, the hip angle HA decreases, for example when sitting down. Conversely, the hip angle HA increases in the case of an extension, for example when standing up or in the case of similar movement sequences.
[0040] During a gait cycle when waking on a level surface, the foot part 30 is placed down heel first, the first contact of the heel or of a heel part of the foot part 30 is called heel strike. A plantar flexion then takes place until the foot part 30 rests completely on the ground, the longitudinal extension of the lower part 10 is here generally behind the vertical, which runs through the ankle joint axis 35. When walking on a level surface, the center of mass is then displaced forward, the lower part 20 pivots forward, the ankle angle AA becomes smaller, and there is an increasing load on the forefoot. The around reaction force vector moves forward from the heel to the forefoot. At the end of the stance phase, a toe-off takes place, which is followed by the swing phase, in which the foot part 30, when walking on a level surface, is displaced behind the center of mass or the hip joint on the ipsilateral side, with a reduction of the knee angle KA, in order then, after a minimum knee angle KA has been reached, to be rotated forward in order then, with a knee joint 1 that is generally extended to the maximum, to achieve heel contact again. The force transmission point PF thus moves during the stance phase from the heel to the forefoot and is illustrated schematically in FIG. 1.
[0041] In FIG. 2, a definition of the leg cords 70 of an ipsilateral, assisted leg and of a contralateral, unassisted leg is given. The leg cord passes through the hip rotation point 16 and forms a line to the ankle joint 35, As can be seen in FIG. 2, the length of the leg cord and the orientation φ.sub.L of the leg cords 70 changes during the movement, in particular also in the case of different gradients. The profile of the change of the length and/or orientation of the leg cords 70 can be used to assess and predict or determine height differences ΔH that are to be overcome. The respective control commands are then derived therefrom. The orientation of the ipsilateral leg cord φ.sub.Li relative to the direction of gravity G as the vertical and of the contralateral leg cord φ.sub.Lk is plotted in each case.
[0042] With reference to FIG. 3, the step height between the contralateral, unassisted leg and the ipsilateral foot part 30 of the assisted leg can be defined. For example, the distance H.sub.1 from the ground to a distinctive point of the hip, for example the hip joint 16 or the trochanter major, at the level of the standing leg is defined, the distance H.sub.2 is the distance between the ground and the hip joint 16 or the trochanter major on the leading side, which in the example shown is the assisted side. The height difference ΔH is then given by the difference between H.sub.1 and H.sub.2. A definition of the height difference ΔH for walking on a ramp applies correspondingly.
[0043] FIG. 4 shows an illustration of different settings of a flexion resistance Rf and a flexion angle Af. The flexion resistance Rf and the flexion angle Af are each set as maximum values. The maximum flexion damping or the maximum flexion resistance Rf remains almost constant when walking down a ramp, when walking on a level surface and on shallow ramps. Only when the downward inclination of the ramp increases is the maximum flexion resistance reduced, for example by 5%. For the situation of walking downstairs, the maximum flexion resistance Rf is then reduced to a substantially lower level, in particular to a level of the stance phase damping for walking on a level surface. The maximum flexion angle Af is likewise changed in dependence on the inclination of the surface. Walking up a ramp and walking on a level surface take place at the same maximum flexion angle Af as in the stance phase. The maximum achievable flexion angle Af is increased in dependence on the surface inclination up to a maximum value, which is set for walking on steep ramps and for walking downstairs. Such stance phase control adjusts the flexion resistance Rf during the early and mid stance phase in dependence on the inclination of the surface and thus also limits the maximum flexion angle within the stance phase. The maximum possible flexion angle Af is adjustable, wherein the limit value is effected by changing the flexion resistance Rf. In dependence on the surface inclination, a maximum target value is specified, at which the flexion resistance Rf has such a high value that no further knee flexion is possible. If the maximum flexion angle Af in dependence on the surface inclination is reached, a different knee angle plateau develops as the movement continues, that is to say when walking on a level surface, on a ramp or when climbing stairs, because further flexion is prevented. If it is recognized that an increased flexion angle is necessary, for example when walking on moderate or steep ramps or when climbing stairs, the flexion resistance Rf is reduced so that an increase of the flexion angle Af is possible also without a plateau, Thus, for example, for climbing stairs, the flexion resistance Rf is reduced to the stance phase damping level.
[0044] FIGS. 5a and 5b show temporal profiles of the flexion angle Af and flexion resistance Rf for different surface inclinations. The left-hand illustration in FIG. 5a shows walking on a level surface, the middle illustration in FIG. 5b shows the profile of the two parameters for walking on shallow ramps, the right-hand diagram in FIG. 5c shows the profile of the parameters when walking on ramps with a moderate inclination. In the illustration of FIG. 5a, a knee flexion is first effected after initial contact, so that the flexion angle Af increases. Together with the increase in the flexion resistance Rf, it is clear from the left-hand third of FIG. 5a that further flexion is suppressed, so that a plateau both of the flexion resistance Rf and of the flexion angle Af occurs. As the gait progression continues, after the roll-over, the flexion angle Af decreases. Then, from a specific limit value, the flexion resistance Rf is reduced in order to allow further flexion at the end of the stance phase, so that a sufficiently large flexion angle Af can be achieved in the swing phase.
[0045] FIG. 5b shows walking on a shallow ramp, Here too, the flexion resistance Rf is increased after the heel strike until further flexion and a further increase of the flexion angle Af is no longer possible. Unlike in FIG. 5a, the plateau phase in the first third of the diagram of FIG. 5b is not followed by an extension but by a roll-over with a flexed knee joint. Such a movement profile is typical for walking downward on a shallow ramp. The flexion resistance Rf is reduced after a defined period of time. The period of time can, for example, be such that, after the heel strike and at a normal walking speed, complete contact with the ground has been achieved by the foot part, Statistical data for the duration of a stance phase and thus also for the first lowering of the flexion resistance Rf can be used to initiate an inflexion. The flexion resistance Rf is lowered, so that a further inflexion and a further increase of the flexion angle Af can take place. Here too, the swing phase is allowed and the flexion resistance Rf is reduced to a minimum value.
[0046] FIG. 5c shows the profile of the parameters on a steeper surface, the plateau phase after the flexion resistance Rf has been increased is very short, the reduction of the flexion resistance Rf for the swing and initiation of the swing phase takes place as in FIG. 5b at the latest possible point in time, in order to obtain sufficient stability in particular when walking downhill. The flat portions in the profile of the knee angle Af are in each case accompanied by slowing of the initial knee flexion owing to the increased flexion resistance Rf. More ground clearance is thus generated during the swing of the contralateral, that is to say unassisted, side. Unnecessary compensating movements on the contralateral side can thus be avoided. The profiles of the flexion resistance Rf between the heel strike or initial heel contact and a renewed extension movement or in the case of a roll-over movement are of particular importance.
[0047] FIG. 6 shows three diagrams for different surface inclinations, the top illustration relates to walking on a level surface, the middle illustration relates to walking down a ramp, and the bottom illustration relates to walking downstairs. In the left-hand diagram in each case, the profiles of the flexion angle Af and the inclination angle or roll angle As of the lower part are shown. In the right-hand illustration in each case, the roll angle As is plotted as the X-component and the flexion angle Af is plotted as the Y-component. Heel contact is marked with a circle in each case, Starting from heel contact, the diagram passes through a closed, two-dimensional curve with in each case characteristic curve profiles. At selected points in time, for example in constant, discrete time portions, the tangential gradient of the curve profile is calculated. For this purpose, the ratio of the flexion angular velocity and the roll angular velocity is calculated continuously. The calculated ratio is optionally smoothed by means of a low-pass filter, wherein the filter is not switched on or initialized until shortly after the heel contact or heel strike, in order to avoid excessive signal interference owing to the initial heel contact. From the heel strike, via the starting stance phase flexion, the calculated and filtered value is assigned via an interpolation function with defined support points to a corresponding ramp inclination. It follows from the illustrations of FIG. 6 that, for each gait situation with different inclinations, different tangential gradients occur at the curve, so that the tangential gradient can be used to determined the surface inclination and to set a corresponding change of the flexion resistance in dependence on the surface inclination.
[0048] FIG. 7 shows three graphs for evaluating the kinematic criterion, that is to say for evaluating the flexion angle Af and the roll angle As of the lower part. The top graph illustrates walking on a level surface, the middle graph illustrates walking on a shallow ramp, the bottom illustration represents walking on a steep ramp. The curve profile of the flexion angle Af corresponds substantially to the profile of the flexion angle of FIGS. 5a to 5c. The profile of the flexion resistance Rf is shown in each case by the solid line, the dashed line is the time-delayed actual value. In the top illustration, the kinematic criterion Kk is set at the value 2 throughout, which corresponds to walking on a level surface. The value 1 corresponds to walking on a moderate ramp, the value 0 corresponds to a steep ramp or a staircase. It can be seen in the top illustration that the kinematic criterion Kk for walking on a level surface shows correct values throughout and provides correspondingly adjusted control of the flexion resistance Rf for the stance phase flexion with the pronounced plateau phase for the flexion angle Af. In the middle graph, it can be seen that the value for the kinematic criterion Kk falls to approximately 1.6, which corresponds to walking on a shallow ramp. As soon as the value of the flexion resistance Rf increases, a self-reinforcement process occurs, which raises the kinematic criterion Kk again in the direction of walking on a level surface. The minimum of the kinematic criterion Kk achieved after the heel strike occurs is therefore crucial for controlling the flexion resistance Rf. In the present case, this leads to an increase in the flexion resistance Rf up to a block at a significantly larger flexion angle Af than in the case of walking on a level surface.
[0049] In the bottom illustration of FIG. 7, it can be seen how the kinematic criterion Kk quickly falls to the value 0 when walking on very steep ramps, which is comparable to walking up stairs. An increase in the flexion resistance Rf is thus avoided, so that further flexion of the knee and an increase in the flexion angle Af are possible without a plateau phase. The surface that is being walked on or the gait situation that is recognized thus leads to significantly different changes of the flexion resistance Rf,
[0050] FIG. 8 illustrates the displacement calculation criterion, which is determined over a defined period of time on the basis of the sensor signals of the IMU. The accelerations at the knee joint 1 or the lower part 20 in the forward direction and upward direction are integrated. The upward direction acts against the direction of gravity, the forward direction is a forward direction in the sagittal plane from posterior to anterior. By means of a single integration over time, the velocities are obtained in each case, by means of a double integration over time of the values of the IMU, the distances travelled in the vertical direction and in the horizontal direction are obtained in each case. In FIG. 8, the horizontal distances travelled are denoted ΔV, the vertical distances travelled are denoted ΔH. The vertical velocities are described with Vv, the horizontal velocities with Vh. FIG. 8 shows walking on a downwardly inclined ramp. The general surface inclination is defined as the ratio of the horizontal distance travelled ΔV to the vertical distance travelled ΔH, wherein the distance travelled is in each case calculated in the vicinity of the sole of the foot. For this purpose, the position of the lower part 2 is determined at the beginning and at the end of the integration, and the distance travelled by the foot relative to the IMU can be calculated by means of the known geometric parameters such as length of the lower part, the position of the IMU on the lower part 20 or on the upper part 10, and the knee angle. Using the displacement calculation criterion, it is also possible to recognize the surface inclination with a comparatively good resolution. The value for the general surface inclination determined by means of the displacement criterion can then be used as a control parameter for adjusting the flexion resistance Rf.
[0051] FIG. 9 shows, in a schematic illustration, an exemplary embodiment of an orthosis having an upper part 10 and a lower part 20 mounted thereon so as to be pivotable about a pivot axis 15, with which the method can likewise be carried out. Between the upper part 10 and the lower part 20 there is formed an artificial knee joint 1, which in the exemplary embodiment shown is arranged laterally to a natural knee joint. In addition to an arrangement of the upper part 10 and lower part 20 on one side relative to a leg, it is also possible for two upper parts and lower parts to be arranged medially and laterally to a natural leg. The lower part 20 has at its distal end a foot part 30 which is mounted so as to be pivotable relative to the lower part 20 about an ankle joint axis 35. The foot part 30 has a foot plate on which a foot or shoe can be supported. Both on the lower part 20 and on the upper part 30 there are arranged fastening devices for fixing to the lower leg or the thigh. Devices for fixing the foot on the foot part 30 can also be arranged on the foot part 30. The fastening devices can be in the form of buckles, belts, clips or the like, in order to allow the orthosis to be releasably placed on the leg of the user and removed again without being damaged. To the upper part 10 there is fastened the resistance device 40, which bears against the upper part 20 and against the lower part 10 and provides an adjustable resistance to pivoting about the pivot axis 15. The sensors and the control device described above in connection with the exemplary embodiment of the prosthesis are correspondingly present also on the orthosis.
